fixes private named constructors

lib/runtime/dart_runtime.js

Index: lib/runtime/dart_runtime.js
diff --git a/lib/runtime/dart_runtime.js b/lib/runtime/dart_runtime.js
index 043c32a06ae42e6762e5c258e778e8a6de5b872a..fce2a35f9f39fdf68d3c551c75314e4e2735b10a 100644
--- a/lib/runtime/dart_runtime.js
+++ b/lib/runtime/dart_runtime.js
@@ -281,9 +281,8 @@ var dart, _js_helper;
    * function with the same name. For example `new SomeClass.name(args)`.
    */
   function defineNamedConstructor(clazz, name) {
-    var shortName = name.startsWith('::') ? name.substring(2) : name;
     var proto = clazz.prototype;
-    var initMethod = proto[clazz.name + '$' + shortName];
+    var initMethod = proto[name];
     var ctor = function() { return initMethod.apply(this, arguments); }
     ctor.prototype = proto;
     clazz[name] = ctor;